Caption: The magic lantern used a concave mirror in back of a light source to direct as much of the light as possible through a small rectangular sheet of glassâa "lantern slide"âon which was the painted or photographic image to be projected, and onward into a lens at the front of the apparatus. The lens was adjusted to optimally focus the plane of the slide at the distance of the projection screen, which could be simply a white wall, and it therefore formed an enlarged image of the slide on the screen. The magic lantern was the ancestor of the modern slide projector. It was invented in China in the second century, and was in existence in Europe by the late 17th century. .